This invention relates generally to circuit interrupting apparatus and, more particularly, to a high-voltage gas-insulated circuit breaker having an improved puffer assembly.
High-voltage power circuit breakers which employ a movable contact and a stationary piston arrangement to provide a puffer assembly that directs a blast of compressed insulating gas into the arc and quickly extinguishes it are well known in the art. A modular puffer-type circuit interrupter which operates in this fashion is disclosed in U.S. Pat. No. 4,101,748, issued Jul. 18, 1978 to J. R. Meyer et al. One of the problems associated with the operation of such puffer assemblies is their inherent characteristic of developing back-pressure during the contact-closing operation of the interrupter. Such back-pressure is produced by the partial vacuum or "negative pressure" created within the puffer chamber when the puffer cylinder moves away from the stationary piston, along with the movable contact, when the latter is returned to its contact-closed position and the insulating gas is unable to flow into and fill the expanding piston chamber quickly enough. The resulting back-pressure is undesirable since it retards the contact-closing operation and puts additional mechanical stress on the linkage system and operating mechanism.
In the prior art circuit breakers, this back-pressure problem was solved by providing check valves in the piston head of the puffer assembly which permitted an in-flow of insulating gas into the puffer chamber during the closing stroke of the interrupter but closed off the chamber during the opening stroke and thus did not interfere with the compression of the gas within the chamber and the resulting arc-extinguishing puffer action when the contacts were being opened. While such check valves were generally satisfactory from a functional standpoint, they complicated the assembly of the circuit interrupters and increased their manufacturing cost. It is also very difficult and expensive to replace malfunctioning or inoperative check valves in the field since the contact and puffer assemblies are in a sealed tank and are thus not readily accessible.